Instructions
Find any obvious markings or price tags that would tip you off to its age or origin.
Lift up the ashtray and look on its underside. Try to find an artist or company signature along with a date.
Examine the ashtray closer for seams. Ashtrays with noticeable seams are typically manufactured items that are newer than ones hand blown without seams.
Determine whether the glass has any ornate designs. Ornate decorations in glass must be done by hand and are often an indication of a piece from an earlier time. Newer ashtrays are much simpler in design and often mass produced.
See if the glass ashtray comes with any sort of stand or additional hardware. Ashtrays from the late 19th and early 20th century were often created to be pieces of furniture. Check the accompanying hardware for dates and creator information.
Bring the piece to an antique dealer. In most cases, a learned antique dealer would be the most knowledgeable as to the details of a particular glass piece.